Thermoplastic resins, in particular, engineering plastics are each known to have an excellent mechanical strength and an excellent impact strength as well as excellent heat resistance. Of those, a polycarbonate resin has been finding use in a variety of fields typified by automobile parts, home appliance parts, OA system parts, and information recording media because the resin has the following characteristics in addition to the above properties: the resin is transparent and excellent in flame retardance. However, the polycarbonate resin having such characteristics has the following drawback: the resin is poor in chemical resistance. Accordingly, the following problem was present: a resin capable of simultaneously satisfying all of such sophisticated properties of an engineering plastic resin, transparency, and chemical resistance cannot be obtained. To overcome this problem, a blend of the polycarbonate resin and a syndiotactic polystyrene-based resin has been known (see, for example, Patent Documents 1 and 2).
However, such binary system including an aromatic polycarbonate resin and the syndiotactic polystyrene-based resin as described in Patent Document 1 inevitably has the following drawbacks: the syndiotactic polystyrene-based resin has insufficient dispersing performance, so a product obtained by the extrusion molding of the system shows large fluctuations in its width and thickness, and the productivity of the product is poor.
In addition, a polycarbonate resin has been recently finding use in the fields of optical functional films typified by an LCD field. However, the polycarbonate resin has a high optical stress coefficient, and is apt to cause birefringence owing to distortion at the time of its extrusion molding. Accordingly, when the resin is applied to a retardation film in which alignment control is performed, the film is produced by a solvent cast method. In general, when light is incident into a substance having birefringence property, the light is divided into two light beams having vibrating directions perpendicular to each other, and the rates at which the light beams travel differ from each other, so an image formation point shifts from the expected one. The polycarbonate resin has been frequently used also in a base film for a diffusion film or lens film, but often involves, for example, the following problem: the image-forming performance of the base film reduces owing to the birefringence property of the resin, so color unevenness or bleeding occurs. In view of the foregoing, the birefringence of the resin is reduced by lowering the line speed of a molding machine upon production of the base film for a diffusion film. However, the method causes a remarkable reduction in productivity of the base film, and involves, for example, the following problems: an increase in cost for the production and an insufficient ability to supply the resin to the molding machine. In addition, when a styrene/acrylic copolymer out of the compatibilization techniques described in Patent Document 2 is used, the dispersing performance of the syndiotactic polystyrene-based resin can be improved, but the copolymer involves the following problems: there arises a difference in refractive index between the aromatic polycarbonate resin and the syndiotactic polystyrene-based resin, and an increase in addition amount of the copolymer reduces the transparency of the binary system formed of the resins.    Patent Document 1: JP 2004-210915 A    Patent Document 2: JP 2004-210916 A